The present invention relates to a method for manufacture of an internal mirror type gas laser tube, and more particularly, to a method of controlling the output power of such gas laser tubes.
It has recently become possible to manufacture an internal mirror type gas laser tube which is small in size and yet has a high power output. Such manufacture is a result of progress in the laser techniques and an improvement in the method of manufacturing the laser tube. The application for lasers of this type has also expanded from experimental use, in the past, to industrial use such as in point of sale (POS), terminals video disks, etc. In the past, laser output was required to be coherent light having an output power higher than certain values such as 1 mW or 2 mW. However, in industrial applications such as POS terminals, video disks, or the like, in addition to the requirement for coherent light, a fairly severe restriction on deviation of laser power output value is imposed on industrial laser products. This is especially true in view of the fact that a large number of such products should have the same or similar characteristics.
The outputs of known practically mass-produced laser tubes show a normal distribution curve about a predetermined output value at the center of the curve. As a result known manufactured laser tubes have a considerably large deviation in power output. Accordingly, in a case where a predetermined value, or a value within a narrow range is required for laser outputs, product yield is generally unsatisfactory.
One approach to obtain a required rated output power has included a method wherein the center of the normal distribution of the laser output is designed to be somewhat higher than the desired rated output. A filter, having an appropriate transmission rate, is mounted outside of the laser tube and reduces the output power to the desired rated output. However, this method has drawbacks in that many kinds of filters, having different transmission rates, are required in order to cover different output values and a structure for mounting the filter is also required. The result is an increase in the cost of the tube and in the work necessary to select a filter having an appropriate transmission rate. These factors decrease mass-producibility.